Increasing variety of services have been provided with the development of communications. A communications system including a voice message center in a communications network is proposed as one of these services.
For example, Japanese patent application laying-open No. 5-292205 (1993), a first prior art, discloses a service which comprises a voice message storing function in a communications network, and transmits stored messages to subscribers. According to this service, it is not necessary for individual subscribers to posses answering machines.
Japanese patent application publication No. 5-66783 (1993), a second prior art, discloses a technique in which messages stored in the center for subscribers are transferred to their cards inserted in receiving terminals. Specifically, when a subscriber inserts a card storing his telephone number in a receiving terminal, the center transfers the message for him to this card. The card stores the message to be converted into a vocal message. It also discloses a technique which carries out paging when an urgent call connection occurs so that the addressee responding to it inserts his card in a receiver to receive the message. Furthermore, it discloses a technique which makes it possible for a subscriber to carry out a conversation with other subscribers through a switching center using wireless equipment incorporated in his card.
In addition, a technique is known which can be utilized when no voice message center is provided in a mobile communications system, but its subscriber has an answering machine connected to a public telephone network. In this case, the mobile communications system sends his message to the answering machine to be stored, and contacts his mobile station when it comes into a service area.
For example, Japanese patent application publication No. 58-53526 (1983), a third prior art, discloses a special service provided when a subscriber has both an answering machine connected to a public network and a mobile station connected to a mobile communications network. When the mobile station does not respond, the mobile switching center transfers a message to his answering machine, and then carries out automatic paging to the mobile station to notice the presence of the message when it comes into a service area, or transfers the message stored in the answering machine to the mobile station.
In addition, a system including an answering machine only in a mobile station is known as a fourth prior art.
These prior arts, however, present the following problems:
(1) In the first prior art, the terminal must be connected to the network (the switching center) each time the user wishes to listen to his message. This presents the following problems: the reproduction of the message is impossible when the line is unavailable; it takes a long time from a request to the reproduction of the message; traffic to the switching center will increase when users reproduce the message multiple times, etc. In addition, since the switching center handles messages from many subscribers, the stored messages must be deleted at fixed intervals. As a result, the message cannot be reproduced after the fixed interval has elapsed from the storing of the message.
(2) The second prior art discloses nothing about measures to be taken when the card cannot be connected to the center. As a result, the subscriber out of service area cannot be informed that a message is present even if an urgent one arrives. Furthermore, there is another problem that the message might be deleted if the subscriber forgets to take action for receiving it when he enters the service area. Another problem is that the message stored at the center cannot be obtained without a series of manual operations such as inserting his card in a receiver.
(3) In the third prior art, the subscriber must have the answering machine connected to the public telephone network besides the mobile station. Furthermore, since the message stored in the answering machine is transferred to the user through the mobile switching center each time requested, there are problems similar to those of item (1). Moreover, since the switching center carries out paging to the mobile station on one hand, and commands the answering machine to reproduce the message on the other hand, a complex program is required.
(4) In the fourth prior art, the mobile station cannot store incoming messages when its power is off, when the line between the mobile station and the network is unavailable, or when the mobile station enters places which the radio wave does not reach such as subways or the shadow of buildings.